Just kidding, system preferences -> Time Machine. Under the icon, there's a huge toggle that says OFF ----| ON. Switch it to off.

Really, you're not explaining the situation too well. I'm not sure you can truly uninstall it as it's basically part of the OS. Do you just want to turn timemachine off, start using a new drive ?? Otherwise, turning the disk to none might help.

Its a known issue where Timemachine keeps asking for an external drive. I already have it off, I already used command to disable it asking for new disks. Nothing works, it still pops up asking for a drive.

You CAN'T uninstall something that Apple has built-in to the OS. Even if you were successful at it, there "might" be additional problem that will come up (not sure what it will be, but it happened to me with different application.)
I would suggest you to do a clean install of Lion/Snow Leopard if you have the time to do so. That will, and should, fix it 100%.

Seong's advice is probably the easiest way for you to fix your problem without screwing something else up. After the reinstall, you'll want to just turn Time Machine off, instead of trying to delete it...

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